Method for producing hydrogenated polygermasilane and hydrogenated polygermasilane

ABSTRACT

A process for preparing hydrogenated polygermasilane as a pure compound or mixture of compounds includes hydrogenating halogenated polygermasilane.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/EP2010/068994, with an international filing date of Dec. 6, 2010 (WO 2011/067417 A1, published Jun. 9, 2011), which is based on German Patent Application No. 10 2009 056 731.3, filed Dec. 4, 2009, the subject matter of which is incorporated by reference.

TECHNICAL FIELD

This disclosure relates to a process for preparing hydrogenated polygermasilane, and also hydrogenated polygermasilane as a pure compound or mixture of compounds.

BACKGROUND

Known processes for preparing polygermasilane are carried out with GeH₄ and short-chain silanes as starting materials, with the consequences first that it is necessary to deal with substances hazardous to health and difficult to handle, that only certain polygermasilanes are accessible, usually multistage syntheses are required, and in these syntheses the yields obtained, especially of long-chain polygermasilanes, are often low. In particular, it has to date not been possible to prepare longer-chain compounds in a targeted way.

Polygermasilanes are disclosed in U.S. 2007/0078252 A1, for example.

It could be helpful to provide a simplified process for preparing hydrogenated polygermasilane that exhibits an improved yield relative to known processes, and also to provide hydrogenated polygermasilane having improved properties.

SUMMARY

We provide a process for preparing hydrogenated polygermasilane as a pure compound or mixture of compounds including hydrogenating halogenated polygermasilane.

We also provide a hydrogenated polygermasilane as a pure compound or mixture of compounds including substituents z including hydrogen, a ratio of z to germanium/silicon of at least 1:1, an averaged formula Si_(a)Ge_(b)Z_(z), where a+b=1 and z is 1≦z≦3, and an average chain length n with 2≦n≦100.

We further provide a silicon-germanium layer produced from the hydrogenated polygermasilane.

We still further provide a method for producing a silicon-germanium layer on a substrate including A) applying a solid or dissolved hydrogenated polygermasilane to a substrate, and B) pyrolyzing the hydrogenated polygermasilane.

DETAILED DESCRIPTION

We provide a process for preparing hydrogenated polygermasilane as a pure compound or mixture of compounds, where halogenated polygermasilane is hydrogenated. Hydrogenated polygermasilane may mean, for example, a pure compound or a mixture of compounds which in each case have at least one direct bond between two germanium atoms and/or between two silicon atoms and/or between one germanium atom and one silicon atom.

The hydrogenated polygermasilane may have substituents Z comprising hydrogen, a ratio of Z to germanium/silicon of at least 1:1, an averaged formula Si_(a)Ge_(b)Z_(z), where a+b=1 and z is selected from 1≦z≦3, preferably 1.5≦z≦3, more preferably 2≦z≦3, and an average chain length n with 2≦n≦100.

The term “pure compound” is understood below to mean that the hydrogenated polygermasilane comprises compounds having no differences in their chain length, if present in their branches and/or in the number and nature of their rings. In other words, only one fraction of hydrogenated polygermasilane is present in a pure compound. “Pure” here is to be understood in accordance with typical fine-chemicals yardsticks. Accordingly, even pure compounds may include small fractions of impurities, examples being traces of carbon or halogens, or small fractions of different hydrogenated polygermasilanes. Small fractions in this context are less than 0.5 mol %, preferably less than 10 ppm.

Analogously, “mixture of compounds” is understood below to mean that the hydrogenated polygermasilane has at least two fractions whose hydrogenated polygermasilanes differ in their chain length, if present in their branches and/or in their nature and number of rings.

Accordingly, either all of the molecules of the pure compound or all of the molecules of the at least two fractions of the mixture of compounds may in each case have at least one direct bond between two germanium atoms and/or between two silicon atoms and/or between one germanium atom and one silicon atom.

We accordingly provide a process for preparing hydrogenated polygermasilane with which for longer-chain polygermasilanes in particular, the yields are increased relative to known preparation processes, and any desired chain lengths are rendered accessible. By virtue of the fact that hydrogenated polygermasilane is prepared from halogenated polygermasilane, the structure present in the halogenated polygermasilane may also be largely retained in the hydrogenated polygermasilane or may be coincident with that structure.

“Largely” in this case means at least 50%. During hydrogenation, however, there may also be rearrangements of the existing structure of the halogenated polygermasilane resulting, for example, in more branches in the hydrogenated polygermasilane than were present in the starting material, the halogenated polygermasilane. However, according to the halogenated polygermasilane from which they are prepared, the hydrogenated polygermasilanes prepared by the process may remain distinguishable.

With the process it is possible to prepare pure compounds or mixtures of compounds of fully hydrogenated polygermasilanes which have Formula Ge_(x)Si_(y)H_(z) with x+y≧2, x+y≧z≧2(x+y)+2. Preparation takes place by hydrogenation of halogenated polygermasilanes of Formula Ge_(x)Si_(y)X_(z) with x+y≧2, X=F, Cl, Br, I or mixtures thereof, x+y≧z≧2(x+y)+2.

It is possible with this process to prepare hydrogenated polygermasilanes and also hydrogenated oligogermasilanes. Hydrogenated oligogermasilanes have a chain length n=x+y which is selected from the range 2≧n≧8. Their empirical formula is Ge_(x)Si_(y)Z_(z) with x+y≧2, x+y≦z≦2(x+y)+2. Hydrogenated polygermasilanes have chain length n=x+y of n>8 and an empirical formula for the mixture of Ge_(x)Si_(y)Z_(z). In principle, chain lengths of 2≦n≦6 are referred to as short-chain, and chain lengths of n>6 as long-chain. By “chain length” is meant the number of silicon atoms and/or germanium atoms joined to one another directly.

The halogenated polygermasilane may be selected from thermally prepared halogenated polygermasilane and plasma-chemically prepared halogenated polygermasilane. Thermally prepared halogenated polygermasilane may have a higher fraction of branches than plasma-chemically prepared halogenated polygermasilane, which may be largely free from branches. The halogenated polygermasilanes may be pure compounds or mixtures of compounds.

A process for preparing plasma-chemically prepared halogenated polygermasilane is disclosed in WO 2010/031390, for example, the subject matter of which is incorporated herein by reference.

The halogenated, more particularly highly halogenated, polygermasilanes may have substituents selected from a group encompassing F, Cl, Br, and I, and mixtures thereof. During hydrogenation, these halogens may be replaced largely completely by H as a substituent. Largely completely here means at least an extent of 50%. The halogen content of the hydrogenated polygermasilane which is prepared by this process may be less than 2 atom %, more particularly less than 1 atom %. A hydrogenated polygermasilane may therefore have exclusively hydrogen, or hydrogen and a halogen, chlorine, for example, as substituents Z.

The chlorine content of a compound or a mixture, i.e., both of chlorinated polygermasilane and a hydrogenated polygermasilane prepared therefrom, is determined by complete digestion of the sample and subsequent titration of the chloride by the method of Mohr. The H content is determined by integration of ¹H NMR spectra, using an internal standard, and comparison of the resultant integrals, where the mixing ratio is known. The molar masses of the halogenated and hydrogenated polygermasilanes, and the average molar mass of the halogenated and hydrogenated polygermasilane mixtures, are determined by freezing-point depression. From the stated variables it is possible to determine the ratio of halogen and/or hydrogen to silicon/germanium.

The halogenated polygermasilane can be reacted with hydridic hydrogenating agents selected from metal hydrides and/or metalloid hydrides. Metal hydrides and/or metalloid hydrides also comprehend mixed metal hydrides and/or metalloid hydrides respectively, in other words hydrides which contain different metals and/or metalloids or a metal and an organic radical. The hydrogenating agents may be selected from a group encompassing MH, MBH₄, MBH_(4-x)R_(x), MAlH₄, AlH_(x)R_(3-x), and suitable mixtures thereof. Examples of such agents are LiAlH₄, DibAlH (diisobutyl=Dib), LiH, and HCl. Preference is given to mild hydrogenating agents which permit hydrogenation of halogenated polygermane without alteration of the germane-silicon backbone.

Hydrogenation may be carried out at a temperature encompassing −60° C. to 200° C. The temperature range may preferably be −30° C. to 40° C., more particularly −10° C. to 25° C. Furthermore, hydrogenation may be carried out at a pressure selected encompassing 1 Pa to 2000 hPa, preferably 1 hPa to 1500 hPa, more preferably 20 hPa to 1200 hPa. Accordingly, gentle hydrogenation conditions are set up with pressures and temperatures lower in comparison to the prior art. In this way, even less-stable halogenated polygermasilanes can be hydrogenated with a good yield and a high conversion rate.

The halogenated polygermasilane can be diluted in a solvent prior to hydrogenation. The solvent in this case is selected such that it is inert toward the halogenated polygermasilane—that is, does not enter into any chemical reaction with it. Inert solvents selected may be alkanes or aromatics, examples being benzene, toluene or hexane. Mixtures of solvents are conceivable as well. Hydrogenation may alternatively be carried out with undissolved halogenated polygermasilane as well.

With this process, therefore, hydrogenated polygermasilane can be prepared in a good yield, in any desired chain length, and with precursors that present little hazard. Moreover, by a suitable selection of the precursors, it is possible largely to dictate the structure of the hydrogenated polygermasilane. Furthermore, a largely complete hydrogenation of the halogenated polygermasilane can be achieved with this process.

Additionally specified is a hydrogenated polygermasilane as a pure compound or mixture of compounds. The hydrogenated polygermasilane has substituents Z comprising hydrogen, a ratio of Z to germanium/silicon of at least 1:1, an averaged formula Si_(a)Ge_(b)Z_(z), where a+b=1 and z is selected from 1≦z≦3, preferably 1.5≦z≦3, more preferably 2≦z≦3, and an average chain length n with 2≦n≦100. A hydrogenated polygermasilane may be, for example, a pure compound or a mixture of compounds which in each case have at least one direct bond between two germanium atoms and/or between two silicon atoms and/or between one germanium atom and one silicon atom.

With regard to the terms “pure compound” and “mixture of compounds,” the statements already made in connection with the process apply analogously. It is the case in turn that “pure” is understood under typical fine-chemicals yardsticks. Accordingly, even pure compounds may include small fractions of impurities, examples being traces of carbon or halogens. Small fractions here are less than 0.5 mol %, preferably less than 10 ppm.

“Chain length” means the number of silicon atoms and/or germanium atoms attached to one another directly. The chain length of the hydrogenated polygermasilane may be selected more particularly from 4≦n≦50, more particularly from 6≦n≦20.

The averaged formula Ge_(a)Si_(b)Z_(z) is to be understood, accordingly, to mean that a germanium atom or a silicon atom in the hydrogenated polygermasilane has on average 1 to 3 substituents Z. Taken into account here are the germanium atoms and silicon atoms both in linear polygermasilanes and also in rings or branched polygermasilanes. A hydrogenated polygermasilane of this kind is suitable for a multiplicity of applications on the basis of its chemical properties.

The hydrogenated polygermasilane may have been prepared by a process according to the statements above. Accordingly it is prepared by hydrogenation of halogenated polygermasilanes. Through the preparation process, therefore, the structure of the hydrogenated polygermasilane may be derivable from the structure of the halogenated polygermasilane or may be coincident with it.

For example, largely linear hydrogenated polygermasilanes may be obtained by hydrogenating plasma-chemically prepared halogenated polygermasilanes or hydrogenated polygermasilanes having a high fraction of branches may be obtained by hydrogenating thermally prepared halogenated polygermasilanes. Hydrogenation may be carried out largely completely, and so the substituents Z in the polygermasilane largely comprise hydrogen. “Largely” here means again a fraction of hydrogen among the substituents of at least 50%. The hydrogenation, however, may also proceed to completion, giving a 100% fraction of hydrogen as substituent Z.

The hydrogenated polygermasilane may have at least 0.0001 mol % of direct bonds between a germanium atom and a silicon atom. Present accordingly is not only a mixture of polygermanes and polysilanes, but rather compounds in pure form and in the form of a mixture that contains both germanium and silicon in their chains.

The hydrogenated polygermasilane may have a fraction of polygermasilane molecules having more than three directly connected germanium atoms and/or silicon atoms, where at least 8%, more particularly more than 11%, of these germanium atoms and silicon atoms are branching sites. The fraction of polygermasilane molecules having more than three directly connected germanium atoms and/or silicon atoms in this case may be a pure compound, or may be a fraction of the hydrogenated polygermasilane in the case of a mixture of compounds. In each case, such polygermasilane molecules have a chain length of n>3. The term “branching sites” refers both to germanium atoms and silicon atoms connected to more than two other germanium atoms and/or silicon atoms, in other words having only one substituent Z or none at all. Branching sites may be determined by ¹H NMR spectra, for example.

The hydrogenated polygermasilane which is a mixture of compounds may in the form of the mixture have a higher solubility than at least one individual compound present in the mixture. Hence, at least one individual component of the mixture has a lower solubility than the individual component in conjunction with the other components of the mixture of compounds. The reason that lies behind this is that the different components of the mixture act mutually as solubilizers. In principle, shorter-chain molecules have a better solubility than their longer counterparts, and so in a mixture of compounds they also improve the solubility of the longer-chain molecules.

The hydrogenated polygermasilane may have a fraction of polygermasilane molecules having more than three directly connected germanium atoms and/or silicon atoms, where these polygermasilane molecules have an averaged formula Si_(a)Ge_(b)Z_(z) where a+b=1 and 1.9≦z≦2.5. More particularly, z may be selected from 2.0≦z≦2.4.

Furthermore, the hydrogenated polygermasilane may have a substituent Z which additionally comprises a halogen. Accordingly, as well as hydrogen, the hydrogenated polygermasilane may also have halogens, examples being F, Br, I or Cl, or mixtures thereof, as substituents. In this case, the fraction of halogen in the hydrogenated polygermasilane may be less than 2 atom %, more particularly less than 1 atom %. We accordingly provide a largely hydrogenated polygermasilane which has only a low fraction of halogen substituents.

Furthermore, the hydrogenated polygermasilane may have a fraction of hydrogen which is greater than 50 atom %, preferably greater than 60 atom %, more particularly greater than 66 atom %. The hydrogenated polygermasilane thus has a very high fraction of hydrogen, whereby the ratio of substituent to silicon/germanium of at least 1:1 is established in conjunction with a high hydrogen content.

In ¹H NMR spectra, the hydrogenated polygermasilane may have significant product signals in the chemical shift range of 6.1 to 2.0 ppm, more particularly 5 to 2.1 ppm. “Significant” in this context means that an integral is greater than 1% of the total integral. Furthermore, in ¹H NMR spectra, the hydrogenated polygermasilane may have at least 80% of the signal intensity of the total integral of its significant product signals in the chemical shift range of 5.0 to 2.9 ppm, more particularly 4.0 to 3.0.

In ²⁹Si NMR spectra, the hydrogenated polygermasilane may have significant product signals in the chemical shift range of −80 to −130 ppm.

Furthermore, in Raman spectra, the hydrogenated polygermane may have significant product bands of 2250 to 2000 wavenumbers and at below 550 wavenumbers. “Significant” in connection with Raman spectra means more than 10% of the intensity of the highest peak.

The hydrogenated polygermasilane may be colorless to yellow or ivory. It may be present as an amorphous or crystalline solid. It is preferably not of high viscosity.

Furthermore, the hydrogenated polygermasilane may be soluble at least to an extent of 20% at concentrations of up to 10% in inert solvents. This means that at least one compound of a mixture of compounds of the hydrogenated polygermasilane is readily soluble in inert solvents. Inert solvents are those solvents which do not react with the hydrogenated polygermasilane. It is possible, for example, to select solvents selected from a group encompassing benzene, toluene, cyclohexane, SiCl₄, and GeCl₄.

The readily soluble hydrogenated polygermasilane of the aforementioned mixture of compounds may be distillable and/or volatile without decomposition to an extent of more than 20%, preferably to an extent of more than 80%, under reduced pressure. The reduced pressure in this case comprises preferably 1 to 100 Pa. Accordingly, the hydrogenated polygermasilane can be isolated effectively.

We additionally provide a silicon-germanium layer produced from a hydrogenated polygermasilane according to the statements above.

The hydrogenated polygermasilane, then, is a starting compound readily available on an industrial scale for production of silicon-germanium layers. As a result of the low pyrolysis temperature of less than 500° C., preferably less than 450° C., the hydrogenated polygermasilane is a single-source precursor with which it is possible, at a low temperature, to deposit silicon-germanium alloys in the form of layers on substrates. The low pyrolysis temperature permits a relatively large selection of materials for the carrier layers and substrates to which silicon-germanium layers are applied, examples being carrier layers of glass. Moreover, diffusion of impurities from the carrier material into the resultant silicon-germanium layer will be diminished or avoided.

Silicon-germanium layers of this kind can be used, for example, in photovoltaics or in the electronics industry. Additionally possible are applications in organometallic chemistry as, for example, for the production of conductive polymers or light-emitting diodes.

A method for producing a silicon-germanium layer on a substrate comprises the method steps of A) applying a solid or dissolved hydrogenated polygermasilane according to the statements above to a substrate and B) pyrolyzing the hydrogenated polygermasilane. This method leads, with high yields and high conversion rates, to silicon-germanium layers produced from hydrogenated polygermasilanes. The hydrogenated polygermasilanes can be processed with a higher yield and a higher conversion rate than conventional mixtures of silicon and germanium precursors, to form silicon-germanium layers. In this context, dissolved or else solid hydrogenated polygermasilanes can be applied in an easy way to the substrate. CVD (chemical gas-phase deposition), PVD (physical gas-phase deposition) or plasma deposition is therefore not necessary. Provided, therefore, is a simplified method for producing silicon-germanium layers.

Indicated below is a working example that relates to preparation of a hydrogenated polygermasilane.

A polychlorogermasilane (PCGS) generated by plasma reaction of GeCl₄ with SiCl₄ and H₂ takes the form of a highly viscous oil or a solid, each with a color of yellow to orange-brown. 8.5 g (60 mmol GeCl₂ equivalents) of the PCGS are admixed with 40 ml of absolute benzene and undergo partial dissolution as a result. At 0° C., 26 ml of diisobutylaluminum hydride (145 mmol, about 20% excess) are added dropwise over the course of 30 minutes. Over the course of about 1 hour, the orange sediment reacts to form a pale yellow powder. The reaction mixture is subsequently stirred for 16 hours, during which it is warmed to room temperature. The solid is isolated by filtration and washed with twice 25 ml of absolute hexane. After drying under reduced pressure, 2.1 g of hydrogenated polygermasilane are isolated.

Our compositions and methods are not restricted by this description on the basis of the working examples. Instead, this disclosure encompasses every new feature and also every combination of features which includes, in particular, any combination of features in the appended claims, even if that feature or that combination is itself not explicitly specified in the claims or working examples. 

1. A process for preparing hydrogenated polygermasilane as a pure compound or mixture of compounds comprising hydrogenating halogenated polygermasilane.
 2. The process according to claim 1, where the halogenated polygermasilane is selected from the group consisting of thermally prepared halogenated polygermasilane and plasma-chemically prepared halogenated polygermasilane.
 3. The process according to claim 1, where the halogenated polygermasilane is reacted with at least one hydridic hydrogenating agent selected from the group consisting of metal hydrides and metalloid hydrides.
 4. The process according to claim 3, where the hydrogenating agents is at least one selected from the group consisting of MH, MBH₄, MBH_(4-x)R_(x), MAlH₄ and AlH_(x)R_(3-x).
 5. The process according to claim 1, where hydrogenation is carried out at a temperature of −60° C. to 200° C.
 6. The process according to claim 1, where hydrogenation is carried out at a pressure of 1 Pa to 2000 hPa.
 7. The process according to claim 1, where the halogenated polygermasilane is diluted in a solvent prior to hydrogenation.
 8. A hydrogenated polygermasilane as a pure compound or mixture of compounds comprising: substituents Z comprising hydrogen, a ratio of Z to germanium/silicon of at least 1:1, an averaged formula Si_(a)Ge_(b)Z_(z), where a+b=1 and z is 1≦z≦3, and an average chain length n with 2≦n≦100.
 9. The hydrogenated polygermasilane according to claim 8, prepared by a process according to claim
 1. 10. The hydrogenated polygermasilane according to claim 8, which has at least 0.0001 mol % of direct bonds between a germanium atom and a silicon atom.
 11. The hydrogenated polygermasilane according to claim 8, having a fraction of polygermasilane molecules having more than three directly connected germanium atoms and/or silicon atoms, where at least 8% of these germanium atoms and/or silicon atoms are branching sites.
 12. The hydrogenated polygermasilane according to claim 8, which is a mixture of compounds where the mixture has a higher solubility than at least one individual compound present in the mixture.
 13. The hydrogenated polygermasilane according to claim 8, having a fraction of polygermasilane molecules having more than three directly connected germanium atoms and/or silicon atoms where the polygermasilane molecules have an averaged formula Si_(a)Ge_(b)Z_(z) where a+b=1 and 1.9≦z≦2.5.
 14. The hydrogenated polygermasilane according to claim 8, where Z additionally comprises halogen.
 15. The hydrogenated polygermasilane according to claim 14, where a fraction of halogen is less than 2 atom %.
 16. The hydrogenated polygermasilane according to claim 8, where a fraction of hydrogen is greater than 50 atom %.
 17. The hydrogenated polygermasilane according to claim 8, which in ¹H NMR spectra has significant product signals in the chemical shift range of 6.1 to 2.0 ppm.
 18. The hydrogenated polygermasilane according to claim 8, which in ¹H NMR spectra has at least 80% of signal intensity of a total integral of its significant product signals in a chemical shift range of 5.0 to 2.9 ppm.
 19. The hydrogenated polygermasilane according to claim 8, which in ²⁹Si NMR spectra has significant product signals in a chemical shift range of −80 to −130 ppm.
 20. The hydrogenated polygermane according to claim 8, which in Raman spectra has significant product bands of 2250 to 2000 wavenumbers and at below 550 wavenumbers.
 21. The hydrogenated polygermasilane according to claim 8, which is colorless to yellow or ivory.
 22. The hydrogenated polygermasilane according to claim 8, which is an amorphous or a crystalline solid.
 23. The hydrogenated polygermasilane according to claim 8, which is soluble at least to an extent of 20% at concentrations of up to 10% in inert solvents.
 24. The hydrogenated polygermasilane according to claim 23, where readily soluble hydrogenated polygermasilane is distillable and/or volatile without decomposition to an extent of more than 20% under reduced pressure.
 25. A silicon-germanium layer produced from a hydrogenated polygermasilane according to claim
 8. 26. A method for producing a silicon-germanium layer on a substrate comprising: A) applying a solid or dissolved hydrogenated polygermasilane according to claim 8 to a substrate; and B) pyrolyzing the hydrogenated polygermasilane. 